> On 11/02/14 03:42 AM, Joeri Casteels wrote: >> I can cranck up the initial sync to 750MB/s when playing with the c-rate’s >> (still not a good performance) while after the initial sync it drops back to >> 400MB/s > > Initial sync is not reflective of real-world performance. In fact, it's kept > low on purpose. > > If your DRBD resource (slowest of the network or drives) is, say, 1.1 GB/sec, > then that is your _replication_ speed. When both nodes are UpToDate, your > applications using the DRBD resource will work at this speed. > > Synchronization speed is the speed at which out of sync blocks are copied to > the peer. So say, for example, your nodes are UpToDate. Then you disconnect > node 2 for a couple of hours and during that time, 50 GB of data changes on > node 1. When node 2 returns, DRBD will start copying that 50 GBs of changes > will start to sync from node 1. This runs at the sync speed. > > If this sync runs at 750 MB/sec, then your apps will feel like their storage > has slowed from 1,100 MB/sec down to just 350 MB/sec (1,1000 - 750). This is > rarely what people want, so the best option is to let the sync operation take > longer and let the application speed stay high. The general rule of thumb is > to set the sync rate no higher that 30% of the tested maximum write speed. > This is a good trade off between syncing quickly without hurting replication > performance too much. > > Make sense?
Yes i know :-) that’s not my problem and after initial sync i do set it to max 30% of the real speed. Initial sync i do without limitations. and then i get about 755MB/s > > Please wait until both nodes are UpToDate and then run your 'dd' test by > writing directly to the /dev/drbdX device (or a file on it's FS, if you > formatted /dev/drbdX). The performance you get with this test will reflect > the performance your apps using DRBD should expect. Here is where the problem is i only get 400MB/s and no more after the nodes are uptodate with oflag=direct If i detach the secondary i’m back at 1.8GB/s with oflag=direct and 1.1GB/s with no flags. I would expect that i get around 1+ G/s with oflag=direct and without around 900MB/s with drbd in-between. > > -- > Digimer > Papers and Projects: https://alteeve.ca/w/ > What if the cure for cancer is trapped in the mind of a person without access > to education? _______________________________________________ drbd-user mailing list [email protected] http://lists.linbit.com/mailman/listinfo/drbd-user
